In the art of converting a coil of sheet steel or other sheet metal into separate strips which are rewound into corresponding separate coils, the wide metal strip or web is usually directed through a slitting unit or a punch press to form the separate strips which are rewound into corresponding coils. A number of various types of rewind apparatus or systems have been either used or proposed, for example, as disclosed in U.S. Pat. Nos. 3,406,924, 3,672,595, 3,817,468 and 4,201,352. As discussed in Pat. Nos. 3,406,924 and 4,201,352 a problem is encountered during rewinding of a plurality of strips which are slit or cut from a web of metal such as sheet steel. This problem results from the fact that the center portion of the web is usually thicker than the longitudinal edge portions of the web due to slight bowing of the mill rolls during the rolling operation. It also appears that during the rolling operation, some portions of the web develop internal stresses different from the stresses within other portions of the web causing some of the resulting strips to elongate slightly relative to other strips after the straightening and slitting operations.
The differences in the strips make it desirable to rewind the strips independently at slightly different speeds and for a uniform drag to be applied to the strips in order to obtain a generally uniform tension in the strips during the rewinding operation. If the strips are not rewound at slightly different speeds, it is necessary to provide for a pit within the floor to accommodate the length build up of depending loops formed by accumulations in the strips due to slightly differential thicknesses and stretch in the strips.
In the above-mentioned Pat. No. 3,406,924, the rewinding of the strips is performed on a slip core rewind mandrel wherein each strip is rewound on a corresponding cylindrical metal core and each core is friction driven on opposite ends by thin drive rings which separate the cores. In above-mentioned Pat. No. 4,201,352, the separate strips are rewound on separate corresponding drums or mandrel sections which expand and contract to regulate the frictional contact between the mandrel sections and the first turns or convolutions of the rewound strips.